The influence of post-growth heat treatment on the optical properties of pulsed laser deposited ZnO thin films

In the present investigation, ZnO thin films were deposited on an ITO coated glass substrate using the Pulsed Laser Deposition technique at different annealing temperatures, from 150 to 300 degrees C. Investigation showed the post-annealing process affected the topological structure and optical properties of ZnO thin films, which were investigated by Atomic Force Microscopy (AFM), and UV-Vis spectroscopies respectively. Temperature-dependent Raman spectroscopy and X-ray Diffraction (XRD) were used to confirm the presence of ZnO material. Surface roughness was analyzed by the AFM technique which indicates that it is slightly affected by annealing temperature. Optical transmittance data showed high transmittance about similar to 70% within the visible region. The direct energy bandgap, complex refractive index, the complex dielectric constant was calculated through transmittance and absorption data. The optical band gap was 3.143 eV, firstly dropped to 3.112 eV and then increased to 3.171 eV with increasing the annealing temperatures. The surface roughness of ZnO thin films was associated with variations in optical band gap, indicating that the post-growth annealing method has a substantial impact.